Skip to Content
Streetsblog USA home
Streetsblog USA home
Log In
Safety

Compelling Evidence That Wider Lanes Make City Streets More Dangerous

3:49 PM EDT on May 27, 2015

The rate of side impact crashes is lowest on urban streets with lanes about 10.5 feet wide -- much narrower than the standard 12 feet. Graph: Dewan Karim
The safest lane width is narrow, but not too narrow. Graph: Academia.edu

The "forgiving highway" approach to traffic engineering holds that wider is safer when it comes to street design. After decades of adherence to these standards, American cities are now criss-crossed by streets with 12-foot wide lanes. As Walkable City author Jeff Speck argued in CityLab last year, this is actually terrible for public safety and the pedestrian environment.

A new study reinforces the argument that cities need to reconsider lane widths and redesign streets accordingly. In a paper to be presented at the Canadian Institute of Traffic Engineers annual conference, author Dewan Masud Karim presents hard evidence that wider lanes increase risk on city streets.

Karim conducted a wide-ranging review of existing research as well as an examination of crash databases in two cities, taking into consideration 190 randomly selected intersections in Tokyo and 70 in Toronto.

Looking at the crash databases, Karim found that collision rates escalate as lane widths exceed about 10.5 feet.

Roads with the widest lanes -- 12 feet or wider -- were associated with greater crash rates and higher impact speeds. Karim also found that crash rates rise as lanes become narrower than about 10 feet, though this does not take impact speeds and crash severity into account. He concluded that there is a sweet spot for lane widths on city streets, between about 10 and 10.5 feet.

In Toronto, where traffic lanes are typically wider than in Tokyo, the average crash impact speed is also 34 percent higher, Karim found, suggesting that wider lanes not only result in more crashes but in more severe crashes.

The "inevitable statistical outcome" of the "wider-is-safer approach is loss of precious life, particularly by vulnerable citizens," Karim concluded.

Stay in touch

Sign up for our free newsletter

More from Streetsblog USA

Want a Better 15-Minute City? Ask Residents What They Really Want

A new study from Bogotá models how other cities can ask a deeper set of questions about how to put essential needs within walking, biking or transit distance.

March 19, 2024

Tuesday’s Headlines Win the Gold

Two articles detail efforts in Paris and Los Angeles to put on (relatively) climate-friendly Olympic games in 2024 and 2028.

March 19, 2024

Monday’s Headlines Drink Your Milkshake

How does a president end wasteful subsidies for the highly profitable fossil fuel industry? Many have tried, but none have succeeded, including Joe Biden.

March 18, 2024

How — and Why — To Start a Neighborhood E-Bike Library

American advocates are loaning out e-bikes to their neighbors — and creating flocks of new riders.

March 18, 2024

What Urbanists’ Doug Burgum Lovefest Reveals About the ‘Why’ Behind Our Advocacy

I am far less interested in talking about Gov. Doug Burgum's politics than talking about his values, and how those values shape his urbanism, and thus the actual lives of the people he governs.

March 15, 2024
See all posts